This section provide background information related to the present disclosure which is not necessarily prior art.
During normal operation, electronic equipment can generate undesirable electromagnetic energy that can interfere with the operation of proximately located electronic equipment due to electromagnetic interference (EMI) transmission by radiation and conduction. The electromagnetic energy can be of a wide range of wavelengths and frequencies. To reduce the problems associated with EMI, sources of undesirable electromagnetic energy may be shielded and electrically grounded. Shielding can be designed to prevent both ingress and egress of electromagnetic energy relative to a housing or other enclosure in which the electronic equipment is disposed. Since such enclosures often include gaps or seams between adjacent access panels and around doors and connectors, effective shielding can be difficult to attain because the gaps in the enclosure permit transference of EMI therethrough. Further, in the case of electrically-conductive metal enclosures, these gaps can inhibit the beneficial Faraday Cage Effect by forming discontinuities in the conductivity of the enclosure which compromise the efficiency of the ground conduction path through the enclosure. Moreover, by presenting an electrical conductivity level at the gaps that is significantly different from that of the enclosure generally, the gaps can act as slot antennae, resulting in the enclosure itself becoming a secondary source of EMI.
EMI gaskets have been developed for use in gaps and around doors to provide a degree of EMI shielding while permitting operation of enclosure doors and access panels and fitting of connectors. To shield EMI effectively, the gasket should be capable of absorbing or reflecting EMI as well as establishing a continuous electrically-conductive path across the gap in which the gasket is disposed. These gaskets can also be used for maintaining electrical continuity across a structure and for excluding from the interior of the device such contaminates as moisture and dust. Once installed, the gaskets essentially close or seal any interface gaps and establish a continuous electrically-conductive path thereacross by conforming under an applied pressure to irregularities between the surfaces. Accordingly, gaskets intended for EMI shielding applications are specified to be of a construction that not only provides electrical surface conductivity even while under compression, but which also has a resiliency allowing the gaskets to conform to the size of the gap.
As used herein, the term “EMI” should be considered to generally include and refer to EMI emissions and radio frequency interference (RFI) emissions, and the term “electromagnetic” should be considered to generally include and refer to electromagnetic and radio frequency from external sources and internal sources. Accordingly, the term shielding (as used herein) generally includes and refers to EMI shielding and RFI shielding, for example, to prevent (or at least reduce) ingress and egress of EMI and RFI relative to a housing or other enclosure in which electronic equipment is disposed.